Magnetic sensors are widely used to detect the speed and direction of movement of a gear or slotted target. Magnetic sensors can be placed within a magnetic field created between a magnet and a gear or slot-patterned target. As the gear rotates, the tooth/slot pattern of the target changes the magnetic field pattern created by the magnet. The magnetic sensor can detect whether the magnet is facing a slot or a tooth by the difference in the magnetic field strength. This difference in magnetic field strength can be detected despite not being in contact with the target.
The magnetic field strength detected by the magnetic sensor is dependent on the space between the magnetic sensor, the magnet, and the gear or slot-patterned target. Therefore, this space must be held constant. If the space between these three components is not held constant, a change will occur in the magnetic field strength detected by the magnetic sensor.
Magnetic sensors are also referred to as proximity sensors and geartooth sensors. There are generally two types of magnetic sensors: Hall sensors and magnetoresistive sensors. Hall sensors can be employed in some sensing applications to detect the magnetic field strength component in a direction perpendicular to the sensing plane of the sensor. Magnetoresistive sensors, on the other hand, are capable of detecting magnetic field strength or angle in a direction within the sensing plane of the magnetoresistive element and perpendicular to its thinnest dimension. Magnetoresistive sensors also offer higher sensitivities and superior performance to that of the Hall sensors. Magnetoresistive sensors come in different types. These are ordinary magnetoresistors (MR), anisotropic magnetoresistors (AMR), giant magnetoresistors (GMR), colossal magnetoresistors (CMR), and so forth.
Several methods using magnetic sensors have been implemented to determine the speed and direction of movement of a gear or other slotted target. In some configurations, two magnetic sensors (e.g., Hall, magnetoresistive, or variable reluctance), for example, can be spaced a fixed distance in order to produce two signals with shifted phase. In such a scenario, the phase shift can be used to calculate the direction of movement of the target. This phase shift is highly dependent on the spacing of the two sensor elements relative to the size and spacing of the target features.
A distinct and different spacing of sensor elements is, therefore, needed for every different target feature size and spacing in order to produce optimum phase shift between signals. The sensor elements must be accurately placed during manufacturing of the sensor package, or are dynamically tuned and adjusted to maintain the phase shift. The resulting sensor system package must also maintain this spacing throughout the operating environment and life of the system. Phase shift errors lead to miscalculation of direction and speed. Attempts to use a given sensor system with targets of different feature size and spacing typically lead to errors.
It is therefore believed that a solution to these problems involves the design and implementation of an improved apparatus and method for determining the speed and direction of slotted-targets, as disclosed in greater detail herein.